1. FIELD OF THE INVENTION
The present invention relates to an industrial method for separation of the two major components in a multicomponent mixture, when said two components have in the binary system a monotectic reaction and there are differences between their densities.
The described method will be shown for the case of Zn/Pb major component mixtures, but its scope is generic.
2. DESCRIPTION OF THE PRIOR ART
Industrial methods for extraction of metals from their ores yield final products the purity whereof varies according to the process employed and the characteristics of the starting ore. A typical case is that of the difference there is between the purity of Zn obtained by an electrolytic process as compared with the electrothermic process. In this last case the typical and major impurity usually is Pb, depending on the starting ore.
An industrially used process for reducing the Pb content in electrothermic Zn is the one described in German Pat. DBP No. 1,142,704 and explained in detail in the literature, but it requires addition of Na as a third element, which is not totally eliminated, as there remains a residual concentration of 0.03% in Zn.
The most frequently used industrial method for purification of electrothermic Zn (removal of lead) is to resort to the properties indicated in the liquid-vapor system diagram of phases (distillation); by means of this process Zn of a purity comparable to the electrolytic product can be obtained.
The method proposed in the present invention serves to obtain an intermediate purity insofar as removal of Pb is concerned and is based on the properties of the solid/liquid equilibrium diagram, as well as on the kinetic type phenomena governing the solid/liquid transformation of the major components binary system; in this particular case, the Zn/Pb system. The advantages of the method proposed arise from the comparison of fusion and vaporization latent heats, thus implying a large reduction in the cost of the process and in the simplicity of equipment construction, operation and maintenance.
It is well known that differences in composition between phases in equilibrium in multicomponent systems cause segregation phenomena in the course of processes involving more than one phase, particularly the solid/liquid type. While in the case wherein a final product having a uniform composition is required, segregation must be avoided, the latter, conveniently promoted, may be used in separation processes. Typical examples thereof are the fractional distillation processes, widely used in chemistry, of non-metal solutions and the zonal fusion purification process. Separation can be more effective in cases in which there is a remarkable difference in density between the solid and the liquid and what is desired is simply to obtain a separation of solid-liquid of different compositions. This separation can be intensified by means of centrifugation.
The present invention is precisely directed to a method which, based on the mechanisms governing the alloy solidification process, enable obtaining a separation of the two major components in a multicomponent alloy, up to an acceptable limit for certain industrial uses. For the method to be effective, it is necessary that said components satisfy the following conditions: (1) that they present a monotectic transformation in the binary system, and (2) that they differ in density. The method will be exemplified for the case of a multicomponent alloy having Zn and Pb as major components, with a Pb content which may be greater or lesser than in the monotectic composition.